Fluorescent compounds can be used to directly stain or label a sample so that the sample can be identified and quantitated. Fluorescent dyes are widely used in biological applications in which a highly sensitive detection reagent is desirable. For example, fluorescent dyes may be added as part of an assay for a biological target analyte. Dyes that are able to preferentially bind to a specific biological component in a sample can be used to determine the presence or quantity of that specific ingredient. Exemplary uses of biological staining include detection of cells or bare nuclei with flow cytometry and in vivo and in vitro imaging applications.
Fluorescent dyes with longer wavelength absorption and emission are particularly useful in conjunction with materials of biological origin such as cells and tissues, where background or inherent fluorescence or absorption often interferes with detection of the added fluorescent dye. Furthermore, biological specimens often have decreasing levels of both absorption and fluorescence emission as the illumination energy approaches the infrared.
Biological stains are often membrane permeant and stain both live and dead cells. Depending on the application, staining of live cells may be preferable. For example, live cell staining can provide information about the rate of cell cycling in a population of cells. Staining of live cells can be achieved using a combination of an organelle or membrane stain and a cell permeant nucleic acid stain.
There exists a need for fluorescent compounds that selectively stain live cells and have emission spectra in the near IR region.